Gravity separation of ore is well known in the art. In this process heavy material having a greater density is separated from lighter material having lesser density. An apparatus known as a “jig” is one device used to effect the separation. Other devices include tables, spirals, sluices, drywashers, highbankers, cones, screws, cyclones, bowls, and magnetic fields. In the conventional jig, water is mixed with the ore, and the combined mixture is pulsed such as by cyclically surging water upward and downward through the fixed bed of ore. The pulsation is designed to cause lighter particles to rise to the top of the mixture, and the wanted heavier particles to migrate downwardly through the mixture. A screen (grate) combined with ragging (such as steel balls and garnet which are placed on top of the screen) act as a filter which downwardly passes the heavier particles while blocking the lighter particles.